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British Lung Foundation
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Peak Flow vs Spirometry results

Hi. I am hoping someone can explain the significance of PF & Spirometry. My peak flow is always 200- 250 and varies very little whilst my spirometry (FEV1/FVC) is restricted but is on the low side of normal at 80/83% predicted. During the past few months, I have been finding increased SOB and difficulty in lying flat yet my Peak Flow remains the same - I don't understand how this can be and what I should do about it.

I don't have asthma but have some minor small airway narrowing + some diaphragm weakness. My consultant promised an appt back in November but it has never arrived and I have no resp nurse follow-up at my GP surgery probably because of my lack of diagnosis.

Hope someone can enlighten me as to how these tests work. Many thanks. Clare

17 Replies


Spirometer is more usually used for COPD.

Peak Flow is more usually used for Asthma.

Peak Flow can also be used for COPD, using a conversion table and a simple equation to give a percentage.

Used as you have used would not give equally correct reading, as the spirometer is based on two readings. The first forced blow, similar to Peak Flow, and then a second longer blow to empty lungs, followed by a simple equation to convert to a predicted figure.

To do your self justice you need to use only one device. Which will fluctuate according to how you feel at the time of the test.

Your results appear to be. mild, your final result will give better answer,

Stopping smoking' exercise, balanced diet will show an improvement.


Thank you Stone for explaining. I had googled hard but could not work it out. Thanks again. Clare


Hi Clare I don't fully understand it either but will do my best. I have asthma and copd and the peak and flow meter is a good indication of asthma but not really of copd. A spirometry test is a better way to measure this. I only ever get a peak and flow reading and my last reading was FEV1 66% lung function. It does sound like you are borderline copd and I would go with the spirometry reading as more accurate.

You need to go back to your doctors and find out what is going on. If you do have copd then you would normally get at least an annual review with a respiratory nurse.

Are you on any meds? Inhalers etc.? As you are having sob (shortness of breath) you need to follow this up. Good luck. x

1 like

Hi Coughalot and thank you. These tests are confusing and I am always surprised that my spirometry is as good as it is when my Peak Flow results are so rubbish but it seems that the PF is not actually representative. I have Eklira & Flutiform and take DMARDS for Lupus.

Do many people buy their own devices to record FEV1/FVC and thus monitor their conditions, I wonder?

Thank you again. Clare


Hi Clare, if you have a peak flow of 200-250 I don't understand why you say you don't have asthma as this is a low reading - Stone and Cough are right that peak flow is a measurement of asthma. I hadn't known before that you can do a conversion from peak flow to give an fev1 reading, no idea how that works, so maybe it could be an indication of copd though your spirometry reading is not so far from normal - mild copd at most.

I have asthma and copd and my peak flow is usually around 330 (though it goes down to around 220 when I have a flare-up). My fev1 is 38%, so my readings are pretty much the reverse of yours, where your peak flow is low in relation to your near normal fev1.

You really should be seeing the consultant. You can get the number of his/her secretary and ask when you will get the appointment - they are usually very helpful. Some trusts seem to be delaying giving appointment dates so that their waiting lists don't appear so long - prioritising targets over clinical need which is not ok.

You don't say if you taking medication for the s.o.b. Not having a diagnosis shouldn't be a reason not to have follow-up by either your gp or a respiratory nurse. 200-250 peak flow is not normal (normal is likely to be around 400 or more, it varies with age, gender, etc) and the reason why yours is lower should be investigated.

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Great reply O2 and much better than mine! Thanks. xx


Thanks Cough, but we all put in our own partial view and together they make up a whole. You take care. :)


You too :) x


Hi O2. Thank you for your reply. I've been told no asthma because of no diurnal dip. I don't wheeze either but for someone of my age (47), slimness and activity, I would expect my PF to be better. No-one has mentioned COPD either . . .

Your comment on waiting times, I think, hits the nail on the head. I go to Birmingham to a very well run Lupus clinic and my appt is decided months in advance and doesn't change. Locally, it's a different story. If you get an appt at all, you have no more than 12 - 14 days notice. I think my Consultant has forgotten about me (for the 3rd time in a year) so yes, I shall make that call.

Thanks for your support, it's really helpful. Clare


You're welcome Clare. If i remember right, i think someone else on the forum had a similar problem in Birmingham (i grew up near there btw, bit of irrelevant information!)

Can you tell me about the diurnal dip please? I assume it means that the peak flow varies at some point in the day. The time considered best for asthmatics is generally around mid-afternoon - that certainly works for me - but I've no idea about dips, it always seemed pretty constant (when i had only asthma) and Ive been lucky in not having s.o.b. problems at night.

Please do get back and let us know how you get on when you finally do see the consultant.

Good luck :)


Hi 02Trees, I have never heard of diurnal dip before either and I have lived with or been an asthma patient myself for 40years.

My peak flow is at its best in the middle of the day too.

My friend has Lupus and her peak flow reading is low


Hi knitter - thanks for your reply, odd we haven't heard of this. Also had asthma long time, about 44 years. Learn something every day :)


Hi O2. To answer your question, I was told to record my PF am and PM. If a difference occurred between the 2 readings (the diurnal dip) then it would be indicative of asthma.

Following your nudge, I just phoned the secretary for my Consultant where I was told there was no record of the previous correspondence with my GP nor subsequent promised appointment! Anyhow, she has given me an appt for next week so thank you for that. I would have waited for a few more weeks before pestering. I'll let you know the outcome. Clare


Wow - result! :) :)

I'll try my PF a.m. and p.m. just to see. No question re the asthma though, much as i'd like there to be.

I'd advise calling the British Lung Foundation helpline - they will probably want to make a time for the following day as they are much busier than before (or have had to cut back on staff). They are brilliant at going through your clinical situation and helping you with questions you need to ask the consultant.

So pleased about the appointment :)



You mentioned Restrictive? the above link explains the difference.

I have Restrictive Lung Disease which can give a good PF but is not worth the breath it uses. I blow 350 but when I blow it is everything I have. With RLD it can be even higher and you can be SOB mainly because there is nothing in reserve whereas COPD can, but because of the obstruction it is not coming out as well as it could.

My diaphragm is paralysed which will give you SOB when FLAT my lung function drops a further 12% when flat.

Have you had a Spiro at the hospital? If so did they test you in the BOX and lying down? Have you had the co2 test?

Be Well


Hi Offcut

That's so interesting to hear and, like you, that initial blow empties my lungs completely. Can I ask if you have ever found out the cause of your paralysed diaphragm? How was it diagnosed? I have had 4 sets of PFT'S in the last 18 months to try to identify the problem. Is the CO2 test for diffusion/transfer factor? I have had that one and it was reduced. My spirometry also shows 12% reduction when supine but for me they call it non-significant. I have done the sniff test at 6 monthly intervals which shows diaphragm weakness at 36 (normal is 65+). What strategies have you used to combat the diaphragm issue? Sometimes I can't even manage food as it impacts on my ability to breathe so much. Hope you can share some tips and thanks again for the reply. Clare


Sorry to say they have no idea as to why or when it went? I did notice when I was on holiday that I was SOB when swimming I could not do it any more. It was found when I had repository failure in 2008 and showed on the xray as a diagonal line and my right lung was pushed up by a third. Which is interesting when a GP checks my lungs and fiddles about on the right. This shows they have not read my notes when I tell them there is no lung that low down now! They did mention that they could pull it down and hold it in place with webbing but as I have other problems PH, Heart etc. they will not do it? plus it would not help the breathing as it will not manipulate the lungs anyway?

Socks, pants and jeans are always put on with me sitting on the bed and pulling the leg across my knee and putting them on with arms stretched out. Looks awkward but works for me in between breaths ;)

I have now got into slip on shoes as doing up laces is no fun as I just stop breathing doing them up. I use a long stainless shoe horn so I do not bend over. If I am under the weather I will sleep in a more sitting position but I do not sleep well anyway in any position. I know I need to lose a few stone and it is slowing coming off but I am exercise intolerant and when the reflux and bloating are playing up it makes it all so much worse.

As for medical advise all I have had from my consultant is "Sorry we do not have a magic pill?" and my GP "Live with it, it is not going to get better!"

What I have found is the diaphragm can be made stronger with controlled breathing exercise, but only if it is working in some way? Mine does not do a thing on the right and the left barely :(

Be Well


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